求助!关于LocationManager.getAllProvider();方法

package com.charho.getbestlocation;
import android.content.Context;
import android.location.LocationManager;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.Toast;
import java.util.Iterator;
import java.util.List;
public class MainActivity extends AppCompatActivity {
private Button buttonGet;
private Button buttonAll;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
buttonAll = (Button) findViewById(R.id.buttonall);
buttonAll.setOnClickListener(new ProviderListener());
}
class ProviderListener implements View.OnClickListener {
@Override
public void onClick(View v) {
LocationManager manager = (LocationManager) MainActivity.this.getSystemService(Context.LOCATION_SERVICE);
List<String> providers = manager.getAllProviders();
for (Iterator iterator = providers.iterator();iterator.hasNext();)
{
String provider = (String) iterator.next();
System.out.println(provider+"");
}
}
}
}
最后返回的只有passive以及gps
而没有network.!